Impedance matching in wave guides



April 11 1950 A. G. Fox

IMPEDANCE MATCHING IN WAVE GUIDES Original Filed July 30, 1942 wvw TOR A. 6. FOX

' A TTORNEV Patented Apr. 11, 1950 UNITED STATES PATENT OFFICE IMPEDANCE MATCHING IN WAVE GUIDES Arthur Gardner Fox, Red Bank, N. J assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York 3 Claims.

This invention relates to guided electromagnetic wave transmission and more particularly to impedance matching in wave guides.

An object of the invention is to connect, without impedance mismatch, an air-filled wave guide and a section of guide having a solid core of dielectric material. Another object is to match a dielectric antenna to an air-filled wave guide.

In accordance with the invention an air-filled wave guide is matched to a section of guide having a solid dielectric core by providing an intermediate sheath which fits around the core for a certain distance and extending the core into the air-filled guide for a certain distance. If the sheath of the section having the dielectric core is omitted, the protruding portion of the core may be used as an antenna.

This is a division of application Serial No. 452,- 851, filed July 30, 1942, now Patent No. 2,432,093, issued December 9, 1947.

The nature of the invention will be more fully understood from the following detailed description and by reference to the accompanying drawing, the single figure of which is a perspective view, partly cut away. of a Wave guide transformer in accordance with the invention.

The figure shows a system for transforming the impedance of a wave guide having a cylindrical sheath 4'! and a solid concentric core 48 of dielectric material to match the impedance of an air-filled guide having a cylindrical sheath 49. The core 48 extends beyond the end of the sheath 4'! for a distance F and extends into the sheath 49 a further distance G. The intermediate cylindrical metallic sheath 59 fits around the portion F of the core 48 and is conductively connected to the sheaths 4'1 and 49 by means of the metallic end plates 5! and 52, respectively.

In order to match one wave guide to another one, or to any other wave medium, it is, in general, necessary to have two independent tuning controls. In the system shown, these controls are the lengths F and G of the dielectric core 48. The proper adjustment may be determined as follows: One of the guides is terminated in its characteristic impedance and wave energy is supplied to the transformer in such a way that it passes through a standing wave detector located in the other guide. Then the distances F and G are adjusted, alternately, to minimize the standing wave. The desired adjustment is attained when the detector indicates an absence of any standing wave.

A special case is the one in which the sheath 4'! and the end plate 5| are omitted. This will generally require a readjustment of the distances F and G in order to get a proper impedance match. The protruding portion of the core 48 may now be used as a dielectric antenna for launching or collecting electromagnetic wave energy.

What is claimed is:

1. In combination, an air-filled wave guide having an end plate with an aperture therein, a device comprising a solid dielectric core which extends through said aperture into said guide for a certain distance, and a metallic sheath which fits around the external portion of said core for a certain distance and is conductively connected to said end plate, said last-mentioned distance being less than the length of said core external to said guide and said distances being chosen to minimize the standing wave in said guide at a selected frequency, thereby providing an impedance match between said guide and said device at said frequency.

2. In combination, an air-filled wave guide having an end plate with an aperture therein, a wave guide comprising a solid dielectric core which extends through said aperture into said air-filled guide for a certain distance, and a metallic sheath which fits around said core for a certain distance and is conductively connected to said end plate, said core being smaller in crosssection than either of said guides, and said distances being chosen to minimize the standing wave in one of said guides at a selected frequency, thereby providing an impedance match between said guides at said frequency.

3. In combination, an air-filled wave guide having an end plate with an aperture therein, a dielectric antenna which extends through said aperture into said guide for a certain distance, and a metallic sheath which fits around the external portion of said antenna for a certain distance and is conductively connected to said end plate, said last-mentioned distance being less than the length of said antenna external to said guide, and said distances being chosen to minimize the standing wave in said guide at a selected frequency, thereby providing an impedance match between said guide and said antenna at said frequency.

ARTHUR GARDNER FOX.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 2,129,711 Southworth Sept. 13, 1938 2,197,123 King Apr. 16, 1940 2,351,895 Allerding June 22, 1944 2,406,402 Ring Aug. 27, 1946 2,460,401 Southworth Feb. 1, 1949 

